what would happen if a grounded pith ball came near the electroscope (to make a pith ball take a piece of aluminum foil and place it on a thread and foil the aluminum up into a ball). Draw where the charges would be.  Try this out, making sure the pith ball doesn’t touch the electroscope.   Now work out what would happen if the pith ball touched the electroscope.  Let the pith ball bounce against the electroscope, and then draw the charges to show why it acts differently (or should act differently) at this point.